Woodworker's Central
Woodworker's Gazette
Gazette Archive 6/11/98

Plate Joinery Part II (continued):
by Chuck Ring

In this installment we'll present material dealing with general operation, general methods of work, and a few precautions regarding the machine and its operation. I had planned to cover methods of work in detail, unconventional uses, sources of supply and new products, but have determined that this months article would be to long to handle all of those subjects in detail.

The Machine
All plate joiners should come with a manual which somewhat explains the principal of operation, safe use, adjustments and fine tuning. Some of the manuals fall short on all but the safety aspects of the machine and its operation. While safety is important I believe most manufacturers of this tool would be well advised to enhance the practical operation and adjustment tips contained in the manual. The main safety point you would do well to keep in mind is the blade is actually a small saw blade(usually with sharp carbide teeth) spinning at many thousands of revolutions per minute. Know where the blade is at all times during operation of the machine and pay close attention to those operations where the blade might exit from an end of the work piece. Be aware that the tool does spew sawdust out all of its orifices and eye protection(and hearing) while operating the machine should be a requirement.

The Blade
Most, if not all, blades come pre-sharpened and installed on the machine. Pay close attention to the cutting action of the blade. If the blade begins to feel "sluggish", smokes, or otherwise gives a clue that it is not cutting at its optimum, then consider cleaning the blade of any pitch or other residue. If this does not bring the quality of the cut up to par, then have the blade sharpened or replace it with a new blade. A blade which is dull or dirty will tend to cut a ragged and oversized slot and you'll be faced with joints which constantly have to be "tweaked" to make them fit or align.

Dust And Chip Collection
Some of the machines have excellent or near so, dust and chip collection features. Some, such as the Skil, are next to non- existent. The DeWalt receives criticism regarding the port for the dust collection bag stopping up. Some users lay the blame on this problem to an aluminum tip which juts down from the top of the housing and appears to partially obstruct the port.

When I found my port and the plastic neck of the dustbag clogging, I examined the neck of the bag and found that the fabric from the bag had become frayed which was allowing chips and sawdust to "bottleneck" and back up into the joiner housing. I turned the dustbag inside out and trimmed all of the excess fabric from the area and I've had no further clogging problems with any wood species. Some users have recommended sawing off or otherwise removing the metal tip and while I have no problem with such removal, the user should keep in mind that the part was probably added as a safety feature to keep prying fingers out of the discharge port and away from the sharp blade. Most users have reported satisfactory result with the vacuum accessories supplied with many of the joiners.

Fine Tuning Slot Depth And Length
Most manuals provide at least rudimentary instructions on how adjustments for cutting different size biscuit slots are to be made and to their credit, most machines come adjusted ready to use from the factory. Get into the habit of checking the accuracy of your machine from time to time and if you change any adjustments, test the accuracy in scrap material before cutting slots in project components. Most machines, once set for adjusted properly will continue to be accurate for may hours of operation.

Dry Fitting Components
I believe it is always an excellent idea to dry fit your components prior to placing adhesives in the slots. Occasionally, when we are in a rush to complete a series of slots, it is easy to fail to plunge to the depth needed to properly seat the biscuit. If a biscuit slot should be to shallow or otherwise not properly machined, then the best time to find out is before the glue and clamps are applied. If the assembly should have slots that are shallow, then it is a simple process to re-cut the slot. If one or more slots are misplaced or mismatched in some way, a patch of working material can be made or a patch from one half of a biscuit can be placed in the slot.

The patches, of whatever material, must be glued in and the glue allowed to cure before the replacement slot is machined. In this way, if the replacement slot cuts into the patch, that part of slot which lays in the patch should be just as strong as the original wood.

Work Surfaces And Machining Slots
The material which is being slotted should be placed on a clean, level and solid surface. For most of my operations, my material is placed on my tablesaw top. Not only is it the flattest surface in my shop, but it is inflexible and will not yield to downward pressure should a component be somewhat bowed. If a back-up is needed for the component, I often use my tablesaw fence to perform that function. Most manuals recommend that the work piece be clamped or otherwise secured to the work surface and I believe this to be valuable advise to the beginning user. However, once you are well acquainted with your machine and do not feel intimidated, you might want to consider dispensing with the clamping to the work surface and instead apply adequate physical pressure to keep the work piece in place. You might want to consider setting aside an area for all of your biscuit joinery operations so that work in that location becomes second nature. Kept clean, this area will enhance the operation and make you a more efficient woodworker.

Since biscuits are relatively inexpensive and since more and bigger biscuits generally make for stronger joints, I have made it my habit to always use the biggest biscuits possible in the greatest number possible in my joints. There is, no doubt a point of diminishing return in this theory and a word of caution is in order....you should try to place all of your slots at least 1/4" from the outside surface of your project components and when possible have at least 3/16" to 1/4" space between layers of biscuits. On 1 1/8" to 1 1/4" thick material I always consider"stacking" two biscuits across the joint. On material which is thicker, I place at least three biscuits across the joint.

Adhesives For Plate Joinery
I have seen everything from construction adhesives(a la Liquid Nails) to waterbased adhesives to polyurethane adhesives used for biscuit joinery. My own experience with biscuits and polyurethane adhesives can be found by accessing the FTP site at http://www.theoak.com. I won't go over the information in this article, other than to say I am confident that polyurethane adhesives and plate joinery make a great team. As to how much glue to use and whether or not to coat the slots and biscuits, I come down on the side of adhesive conservation and say that as long as a good coating of adhesive on the walls and bottoms of the slots is applied, anything more is excessive and perhaps wasteful. Each individual will have to decide what is best for his or her process. Once the components are assembled and clamped, they should remain so until there is no danger of the glue not having cured. Here the nature of the adhesive must be taken into account and in some cases(some polyurethane adhesives) a clamping time of up to twelve hours might not be excessive. If there is any question as to whether or not the adhesive is sufficiently cured when the clamps are removed, then care should be taken not to stress the joints.

Next Installment
In the next installment, one of the subject areas we will attempt to cover is special application biscuits and accessories. I ask that you access The Woodworker's Journal for a splendid article and Woodhaven for their biscuits and special tooling for their biscuits. To get a look at their products, you'll have to order a catalog online. Unfortunantly, their site still doesn't offer much in the way of content. I will provide information in the next installment beyond that which is found in the referenced article or on Woodhaven's site. The supplemental information will deal with my testing and use of many of the products.

Chuck Ring

Editor's note: Chuck Ring runs his own woodworking business, occasionally teaches novices the ins and outs of biscuit joinery and is one of the founders of the WWA. He can be reached at cring@concentric.net

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